The present disclosure relates to a motor control device that realizes sensorless drive of a permanent magnet motor, and more particularly to such a motor control device that enables sinusoidal drive of the permanent magnet motor.
Brushless motors have recently been used with household appliances and industrial equipment for their superior efficiency. JP-A1-001-039358, JP-A-2003-339143 and JP-A-2004-242417 all disclose brushless motors used as spindle motors for driving a disc recording medium such as a digital versatile disc (DVD), a compact disc (CD) and a hard disc drive (HDD). A driving device described in each gazette includes Hall elements for detecting a rotor position of the brushless motor and is arranged to generate an energizing signal by a 120-degree energization mode or sinusoidal pulse width modulation (PWM) mode.
Each of JP-A-H09-74790, JP-A-H10-75597 and JP-A-H10-290592 discloses a driving device including Hall elements for detecting a rotational position of the rotor of the brushless motor and is arranged to generate an energizing signal by the sinusoidal PWM mode on the basis of the detected position signal.
The sensorless drive that is employed for miniaturization and low cost of the motor needs to be compatible with the sinusoidal drive for reduction in oscillation and noise in the aforementioned household appliances and industrial equipment. However, the arrangement of a motor control device becomes complicated and accordingly, the cost thereof is increased when operation such as sensorless vector control is carried out using a high-speed processor such as a digital signal processor (DSP).
JP-A-01-8890 discloses a sensorless drive system with a relatively simpler arrangement. Current is caused to flow through two of three phases while the other phase is kept open. Zero cross of an induced voltage is detected by comparison of voltage of the open phase and a reference voltage. A phase to be energized is determined on the basis of the detected zero cross. However, since this system necessitates an open phase, continuous energization such as by use of sinusoidal waveform is impossible, whereupon production of oscillation and noise is inevitable.